If you eat an 'excessive' amount of fat and protein, in all probability tissue will accumulate. If you somehow manage to gorge on fatty porkchops, you will probably gain weight. Whether there's a difference in food efficiency or not--I don't think this has been fully explored. At any rate, this is the most back-handed expression of metabolic advantage I think I've seen.

In theory, mimics starvation. Mechanick doesn't know the theory (in the sense of a body of knowledge), or conflates it with a hare-brained hypothesis. It's well established fact that the keto diet mimics starvation while not being identical to it--the whole point is mimicking the metabolic state of starvation while sustaining the body. It's entirely possible to increase both body fat and muscle without eating carbohydrate, this is an observed fact.